Invasive species are a major cause of biodiversity loss worldwide, but their impact on communities and the mechanisms driving those impacts are varied and not well understood. This study employs functional diversity metrics and guilds—suites of species with similar traits—to assess the influence of an invasive tree (Tamarix spp.) on riparian plant communities in the southwestern United States. We asked: (1) What traits define riparian plant guilds in this system? (2) How do the abundances of guilds vary along gradients of Tamarix cover and abiotic conditions? (3) How does the functional diversity of the plant community respond to the gradients of Tamarix cover and abiotic conditions? We found nine distinct guilds primarily defined by reproductive strategy, as well as growth form, height, seed weight, specific leaf area, drought and anaerobic tolerance. Guild abundance varied along a covarying gradient of local and regional environmental factors and Tamarix cover. Guilds relying on sexual reproduction, in particular, those producing many light seeds over a long period of time were more strongly associated with drier sites and higher Tamarix cover. Tamarix itself appeared to facilitate more shade-tolerant species with higher specific leaf areas than would be expected in resource-poor environments. Additionally, we found a high degree of specialization (low functional diversity) in the wettest, most flood-prone, lowest Tamarix cover sites as well as in the driest, most stable, highest Tamarix cover sites. These guilds can be used to anticipate plant community response to restoration efforts and in selecting appropriate species for revegetation.

入侵物种是世界范围内生物多样性丧失的主要原因，但它们对社区的影响以及导致这些影响的机制各不相同，并且尚未得到很好的理解。本研究采用功能多样性指标和行会（具有相似特征的物种套件）来评估入侵树木 ( Tamarix spp.) 对美国西南部河岸植物群落的影响。我们问：（1）什么特征定义了这个系统中的河岸植物行会？(2) 公会的丰度如何随着柽柳覆盖度和非生物条件的梯度变化？(3) 植物群落的功能多样性如何响应柽柳的梯度覆盖和非生物条件？我们发现了九个主要由繁殖策略以及生长形式、高度、种子重量、比叶面积、干旱和厌氧耐受性定义的不同行会。公会丰度随着当地和区域环境因素和柽柳覆盖率的共变梯度而变化。依靠有性繁殖的公会，特别是那些长期生产大量轻质种子的公会，与较干燥的地点和较高的柽柳覆盖率有更密切的联系。柽柳它本身似乎促进了比资源贫乏环境中预期的具有更高特定叶面积的更多耐荫物种。此外，我们在最潮湿、最易发生洪水、最低的柽柳覆盖地点以及最干燥、最稳定、最高的柽柳覆盖地点发现了高度的专业化（低功能多样性）。这些行会可用于预测植物群落对恢复工作的反应以及选择合适的重新植被物种。